Laser annealing method and laser annealing device

Abstract

The energy distribution in the short-side direction of a rectangular laser beam applied to an amorphous semiconductor film (amorphous silicon film) is uniformized. It is possible to the energy distribution in the short-side direction of the rectangular laser beam by the use of a cylindrical lens array 26 or a light guide 36 and concentrating optical systems 28 and 44 or by the use of an optical system including a diffracting optical element. Accordingly, since the effective energy range of a laser beam applied to the amorphous semiconductor film is widened and the transport speed of a substrate 3 can be enhanced as much, it is possible to improve the processing ability of the laser annealing.

1. A laser annealing method of reforming an amorphous semiconductor film into a polycrystalline semiconductor film by concentrating a laser beam emitted from a solid laser source into a rectangular laser beam on a surface of the amorphous semiconductor film and applying the rectangular laser beam thereto while moving the rectangular laser beam relative to the amorphous semiconductor film in a short-side direction of the rectangular laser beam, comprising:
 uniformizing an energy distribution in the short-side direction of the rectangular laser beam by dividing the laser beam into divided laser beams through a light guide and focusing the divided laser beams through a Y-direction end transferring optical system including two cylindrical lenses; and 
 applying the rectangular laser beam to the amorphous semiconductor film, 
 wherein a Y-direction coherence reducing optical system, which includes a first transparent glass plate and a second transparent glass plate, is provided between the two cylindrical lenses, and 
 wherein a length of the first transparent glass plate is different from a length of the second transparent glass plate. 
 
     
     
       2. A laser annealing device for reforming an amorphous semiconductor film into a polycrystalline semiconductor film by concentrating a laser beam emitted from a solid laser source into a rectangular laser beam on a surface of the amorphous semiconductor film and applying the rectangular laser beam thereto while moving the rectangular laser beam relative to the amorphous semiconductor film in a short-side direction of the rectangular laser beam, comprising:
 a short-side-direction uniformizing means for uniformizing an energy distribution in a short-side direction of the rectangular laser beam, short-side-direction uniformizing means being disposed in an optical path of the laser beam, wherein the short-side-direction uniformizing means includes:
 a light guide; and 
 a Y-direction end transferring optical system, which includes two cylindrical lenses, through which laser beams divided by the light guide pass; and 
 a Y-direction coherence reducing optical system, which includes a first transparent glass plate and a second transparent glass plate, between the two cylindrical lenses, and 
 wherein a length of the first transparent glass plate is different from a length of the second transparent glass plate. 
 
 
     
     
       3. The laser annealing device according to  claim 2 ,
 wherein the light guide is formed of a transparent member having a solid parallel hexahedral shape, and includes X-direction reflecting surfaces facing each other with a distance therebetween in an X-direction, and Y-direction reflecting surfaces facing each other with a distance therebetween in a Y-direction. 
 
     
     
       4. The laser annealing device according to  claim 2 ,
 wherein the short-side-direction uniformizing means is an optical system including a diffracting optical element. 
 
     
     
       5. The laser annealing device according to  claim 2 ,
 wherein the amorphous semiconductor film is an amorphous silicon film. 
 
     
     
       6. The laser annealing device according to  claim 2 ,
 wherein the solid laser source is one of an Nd:YAG laser, an Nd:YLF laser, an Nd:YVO 4  laser, an Nd:glass laser, an Yb:YAG laser, an Yb:YLF laser, an Yb:YVO 4  laser, and an Yb:glass laser. 
 
     
     
       7. The laser annealing device according to  claim 2 , wherein an energy distribution of the rectangular laser beam has a flat top shape having an energy of 430 mJ/cm 2  or more and having a width of 50 μm or more. 
     
     
       8. The laser annealing device according to  claim 2 , wherein a difference between the length of the first transparent glass plate and the length of the second transparent glass plate is more than a coherent length of the laser beam. 
     
     
       9. The laser annealing device according to  claim 2 , further comprising:
 an X-direction end transferring optical system, which includes a first cylindrical lens and a second cylindrical lens, between the two cylindrical lenses; and 
 an X-direction coherence reducing optical system, which includes a third glass plate and a fourth glass plate, between the first cylindrical lens and the second cylindrical lens, 
 wherein the X-direction coherence reducing optical system and the Y-direction coherence reducing optical system are between the first cylindrical lens and the second cylindrical lens. 
 
     
     
       10. The laser annealing device according to  claim 2 , wherein the overlap ratio of the rectangular laser beam is 91 to 95%. 
     
     
       11. The laser annealing device according to  claim 2 , wherein a length in the short-side direction of the rectangular laser beam is several tens of micrometers (μm). 
     
     
       12. The laser annealing device according to  claim 2 , further comprising:
 a beam expander including a concave spherical lens between the solid laser source and the light guide; and 
 an incidence lens between the beam expander and the light guide.